1. Field of the Invention
The present invention relates to water gel explosive compositions and particularly to incorporating therewith a sensitizing amount of a sensitizing agent which comprises aluminum admixed with densifying agents, such as ferrophosphorus and other ferro-materials. In another aspect, the subject invention relates to a novel composition and method to increase the air gap sensitivity and low temperature detonability of water gel explosive compositions. In still a further aspect, the invention relates to a water gel explosive composition sensitized with a sensitizing agent formed by the mixing of aluminum with densifying agents prior to incorporation of the sensitizing agent so formed with the other components of the water gel explosive.
2. Background Art
Water gel explosives have become quite important in the blasting industry. Water gel explosive compositions are well known and generally comprise an oxygen-supplying salt, water which acts as a solvent or carrier for the salt, sensitizers and a thickener, such as guar gum. Additional components which can be utilized include a cross-linker such as sodium dichromate, potassium dichromate or zinc chromate, a fuel which may be water-soluble or water-insoluble, explosive or nonexplosive fuel and auxiliary sensitizers. Insoluble fuels include finely divided ferrophosphorus, sulfur, or carbonaceous material. Soluble fuels include glycol, diethylene glycol, dioxane, diethylene glycol monoethyl ether sucrose, urea or thiourea.
One problem that continues to face the industry is the production of high density, small diameter, water gel explosive compositions with reliable detonation characteristics. Prior attempts to solve this problem have required the use of high concentrations of expensive ingredients such as sodium perchlorate as illustrated by U.S. Pat. No. 3,765,967, issued to Funk, et al. on Oct. 16, 1973 and entitled "Liquid and Slurry Explosives of Controlled High Sensitivity." Metal fuels such as paint grade aluminum, finely divided magnesium, ferrophosphorus, and ferrosilicon may be added to increase the heat generation, and strength of water gel explosive compositions as disclosed in U.S. Pat. No. 3,129,126, issued to Carlevato on Apr. 14, 1964 and entitled "Blasting Composition"; U.S. Pat. No. 3,617,404, issued to Lyerly on Nov. 2, 1971 and entitled "Slurry Explosives Containing the Combination of Nitrogen - Base Salt and Hard Solid Particles as Sensitizer"; U.S. Pat. No. 3,728,175, issued to Craig on Apr. 17, 1973 and entitled "Slurry Explosives"; and U.S. Pat. No. 3,784,421, issued to Craig on Jan. 8, 1974 and entitled "Slurry Explosives Crosslinked With a Compound of Tellurium VI." Metallic phosphides such as manganese phosphide and iron phosphide have been added to priming compounds to vary their speed and sensitivity, as disclosed in U.S. Pat. No. 2,132,996, issued to Palmieri on Oct. 11, 1938 and entitled "Ignition and Priming Compound".
In order to better tailor water gel explosive compositions to conditions at the blasting site, such as diameter of the blasting hole and water content of the blasting hole, the background art discloses the mixing of gel explosives at the blasting site, as in U.S. Pat. Nos. 3,390,032, issued to Albert on June 25, 1968 and entitled "Gelled Aqueous Slurry Explosive Composition Containing As a Gas Generating Agent a Carbonate or Bicarbonate With a Nitrite"; and U.S. Pat. No. 3,465,675, issued to Bronstein on Sept. 9, 1969 and entitled "Process Of Blasting With Thickened Slurried Inorganic Oxidizer Salt Alcohol, Water Explosive Mixtures." In particular, U.S. Pat. No. 3,465,675 discloses the mixing of a water gel explosive at the blasting site and discloses that the slurry can include an active metal fuel such as aluminum in particulate, granular, atomized or flaked form. Also disclosed therein is that other metal fuels may be used alone or in conjunction with aluminum. These metal fuels include ferrosilicon, magnesium, beryllium and lithium.
While paint grade aluminum has been used in water gel explosive compositions to render them cap sensitive, prior compositions were limited by the maximum achievable sensitivity, rendering them unsuitable for certain important applications. In this regard, it has been difficult to achieve adequate cap sensitivity at temperatures at or below 40.degree. or 50.degree. F. even when up to about 7.5% paint grade aluminum was employed. Additionally, compositions utilizing paint grade aluminum to sensitize water gel explosive compositions often had difficulty in detonating across a three-inch air gap in the standard half cartridge test. This test is required by the Bureau of Mines for explosives which are to be employed in underground coal mining applications. Basically, the test requires that one-half of a cartridge of explosive be able to detonate the second half across an air gap of at least 3 inches.
Water gel cap sensitive explosive compositions have also been sensitized by other materials such as some type of alkyl or alkanol amine nitrate. In order to provide a suitable amine nitrate component in these explosive compositions, highly concentrated aqueous solutions of amine nitrate compositions were required. This sensitizer, although very effective, has the disadvantage of being easily detonated by relatively low mechanical impulses. Thus, preparation of a water gel explosive composition sensitized solely by large amounts of an amine nitrate component can be extremely dangerous unless performed with care. In summary, while it is well known that metals such as aluminum, magnesium and zinc can sensitize water gel explosive compositions if used in a sufficiently fine particle size, the use of ferrophosphorous, ferromanganese, ferrosilicon has not been revealed to sensitize water gel explosive compositions. Ferrophosphorous, ferrosilicon and ferromanganese have been considered in the art to be densifying agents and/or fuels as disclosed in U.S. Pat. No. 3,899,374.
Thus, there has remained a continuing need for a high density small diameter water gel explosive composition which possess good low temperature and air gap sensitivity and which could be manufactured at a reasonable cost. The present invention is addressed to remeding these deficiencies by providing a water gel explosive composition and process for preparing the same which results in significantly greater air gap sensitivity and low temperature detonability.